Function callback_arg_binding 

pub fn callback_arg_binding(component: &str, prop: &str, index: usize) -> String

Where a callback prop’s own declared parameters are kept, per instance — the twin of listener_arg_binding for a handler whose target varies by placement instead of being fixed at the component’s own declaration. Typed by the prop’s own function type, which every action bound to it is required to match exactly, so one map serves every target the tag can name.